Commutator construction



Jan. 15, 1963 D. B. HOOVER COMMUTATOR CONSTRUCTION Filed Nov. 14, 1960 ATTORNEY T Fig. l.

Fig. 2.

NESSES= INVENTOR 7 1M ,Qillon B.Hoover "BY 9 4 x 2 22 24 67 w United States Patent "ice The present invention relates to commutator-type rotor members for dynamoelectric machines, and more particu larly to commutators which are used in high speed turbogenerator exciters.

In commutator constructions of the type to which the present invention relates, it has been customary to fill the space under the coil ends between the commutator riser and the front end of the rotor core, and also the circumferential spaces between the commutator risers, with a heat hardenng, asbestos filling compound or cement. This expedient has been practiced for some time, because of the necessity for preventing conducting deposits from forming back of the commutator risers. This construction has been employed in order to prevent dirt laden air from passing back through the spaces between the commutator risers and depositing a layer of electrically conducting dirt on the parts between the armature core and the commutator risers and ultimately providing a shortcircuiting path of relatively low resistance to ground. Without the filling these places were diflicult to clean and the creepage distance from the commutator riser to ground is limited. 1

This construction has resulted in a considerable increase in the temperature of the commutator. Furthermore the packing used has been difficult to apply and often develops flaws. One of the difiiculties in applying the cement packing has been the necessity for applying the packing after the material is assembled on the shaft. This is necessary because the cement packing material requires support all around. It is therefore necessary to fill all the space intermediate the commutator riser and the space under the coil end. It is necessary to fill the entire space at one time because separate applications of cement would form joints between the cement which are somewhat weak.

The principal object of the present invention is to pro vide an improved commutator construction for a dynamoelectric machine which permits free passage of air around the coil ends.

Another object of the present invention is to provide an improved commutator construction for dynamoelectric machines which facilitates cleaning of conducting deposits from between the armature core and the back side of the commutator riser and also from the coil ends.

A further object of the present invention is to provide an improved commutator construction for a dynamoelectric machne in which long insulation creepage distance is provided from the commutator bars to grounded parts of the machine.

A still further and more specific object of the invention is to provide an improved commutator construction for a dynamoeleetrie machine which utilizes insulating banding between the commutator riser and grounded parts, thereby providing long insulation creepage distance between commutator bars and grounded parts, and which also provides a smooth cylindrical surface which is easy to clean and which permits free flow of ventilation air around the coil ends. I

Other objects and advantages of the invention will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is a fragmentary longitudinal section of a portion of a dynamoelectric machine illustrating the invention; and

3,073,980 Patented Jan. 15, 1963 FIG. 2 is a fragmentary transverse sectional view along the line II-II in FIGURE 1.

The invention is shown applied to a dynamoelectric machine 10 having a stator member indicated at 12 and a rotor member 14. The rotor 14 has a core 16 mounted on a shaft 18. Spaced axially from the front end of the rotor core is a commutator 20 which is illustrated as comprising a plurality of commutator bars 22 and mica bars 24 which are held in place by front shrink rings 26, one of which is shown, and a rear shrink ring 28. Rear shrink ring 28 is centered and supported within an annular centering plate 30 which constitutes annular means for supporting the commutator for rotation with the rotor core. The centering plate 30 is supported on the commutator shell 32 which is a sleeve mounted on the shaft 18, in accordance with the known construction. At each end of the rotor core 16 is an end plate 34 for retaining the rotor laminations in position. The end plate 34 has a plurality of axially extending lugs 36 disposed about its circumference. Secured to the lugs 36 is an annular ring 38, preferably of insulating material, which constitutes a coil support.

The commutator 20 is also provided with aplurality of commutator risers 40 which are centered circumferentially in the bars 22. The commutator risers are set into and suitably and securely fastened within suitable sockets 42 in the respective bars, in accordance with the known construction. The top portions of the risers 40 are electrically connected to the front ends 44 30 of the armature coils or winding.

In accordance with the invention, substantially impervious insulating tape or banding 50 is Wound about the commutator bars 22 and a substantial number of layers 51 of the tape 50 are wound to cover the outer surface 52 of the centering plate. The upper layers 51 extend from the rear of the riser bars 40 to a point adjacent the inner edge of the centering plate 30. The insulating banding 50 is preferably glass tape or roving impregnated with a suitable polyester resin, but may be any suitable impervious insulating tape. The banding 50 occupies the volume between the commutator risers and the rear shrink ring 28 as well as covering the center plate 30. This gives extra long insulation creepage distance from the commutator bars to the grounded centering plate 30. The area between the shrink ring 28 and the commutator risers 40 is easy to clean since the surface is accessible and is of a smooth cylindrical shape. In this construction, the coil ends are left open to permit easy cleaning of the coil ends and free passage of air around the coil ends.

Experience has shown that the present invention results in as good if not better prevention of short circuiting deposits by dust, dirt and ventilating air as previously used constructions. It simplifies cleaning of the coil ends and the portions under the coil ends.

Another advantageous feature of this invention is that the commutator assembly including the commutator bars 22, the risers 40, the centering plate 30 and shrink rings 26 and 28 can be assembled together. The banding 50 can be applied to the commutator assembly prior to mounting on the shaft. This simplifies manufacture considerably.

In previous constructions used it was necessary to introduce the cement packing subsequent to the mounting of the commutator assembly on the rotor shaft 18. The present invention eliminates the possibility of cracks and flaws in the insulating medium. The cement filling of prior constructions was subject to flaws and cracks which seriously impaired both the mechanical and electrical strength.

It should now be apparent that an improved commutator construction for dynamoelectric machines has been provided which permits free passage of air around the coil ends due to elimination of packing material in the filling space under the coil ends. It should also be apparent that due to the smooth cylindrical surface provided by the insulating tape or banding 50, cleaning of conducting deposits in the commutator area has been facilitated and a long insulating creepage path between the commutator bars and the grounded parts is provided by the banding 50. It should also be apparent from the above description that a free flow of ventilation air over the coil end is now introduced.

A particular embodiment of the invention has been shown and described for the purpose of illustration but'it wil be apparent that various other embodiments of the invention are possible within the scope of the invention.

I claim as my invention:

1. A commutator-type dynamoelectric machine having a rotor-core, an armature-winding carried by the rotor core, a commutator spaced axially from the front end of the rotor core, commutator riser bars extending radially outward from the commutator, annular means for supporting said commutator for rotation with said rotor core, and insulating banding wrapped around said commutator and occupying the space intermediate said risers and said annular means to forman uninterrupted, smooth cylindrical surface between the risers and said annular means.

2. A commutator-type dynamoelectric machine having a rotor-core, an armature winding carried by the rotor core, a commutator spaced axially from the front end of V the rotor core, commutator riser bars extending radially outward from the commutator, annular means for supporting said commutator for rotation with said rotor core, and glass polyester banding wrapped around said commutator and occupying the space intermediate said risers and said annular means to form a smooth, uninterrupted surface between the risers and said annular means.

3. A commutator-type dynamoelectric machine having a. rotor-core, an armature winding carried by the rotor core, a commutator spaced axially from the front end of the rotor core, commutator riser bars extending radially outward from the commutator, annular means for supporting said commutator for rotation with safd rotor core, insulating banding wrapped around said commutator and occupying the space intermediate said risers and said annular means, said insulating banding also extending over the outer surface of said annular means to form a smooth, uninterrupted surface between the risers and said annular means.

4. A commutator-type dynamoelectric machine having a rotor-core, an armature winding carried by the rotor core, a commutator spaced axially from the front end of the rotor core, commutator riser bars extending radially outward from the commutator, annular means for supporting said commutator for rotation with said rotor core, glass polyester banding wrapped around said commutator and occupying the space intermediate said risers and said annular means, said banding also extending over the outer surface of said annular means to form a smooth, uninterrupted surface between the risers and said annular means.

References Cited in the file of this patent UNITED STATES PATENTS Kreh Jan. 5, 1943 Axelson July 21, 1959 OTHER REFERENCES 

1. A COMMUTATOR-TYPE DYNAMOELECTRIC MACHINE HAVING A ROTOR-CORE, AN ARMATURE-WINDING CARRIED BY THE ROTOR CORE, A COMMUTATOR SPACED AXIALLY FROM THE FRONT END OF THE ROTOR CORE, COMMUTATOR RISER BARS EXTENDING RADIALLY OUTWARD FROM THE COMMUTATOR, ANNULAR MEANS FOR SUPPORTING SAID COMMUTATOR FOR ROTATION WITH SAID ROTOR CORE, AND INSULATING BANDING WRAPPED AROUND SAID COMMUTATOR AND OCCUPYING THE SPACE INTERMEDIATE SAID RISERS AND SAID ANNULAR MEANS TO FORM AN UNINTERRUPTED, SMOOTH CYLINDRICAL SURFACE BETWEEN THE RISERS AND SAID ANNULAR MEANS. 